Interface energetics, alteration

Highlights of research results from the chemical derivatization of n-type semiconductors with (1,1 -ferrocenediyl)dimethylsilane, , and its dichloro analogue, II, and from the derivatization of p-type semiconductors with N,N -bis[3-trimethoxysilyl)-propyl]-4,4 -bipyridinium dibromide, III are presented. Research shows that molecular derivatization with II can be used to suppress photo-anodic corrosion of n-type Si derivatization of p-type Si with III can be used to improve photoreduction kinetics for horseheart ferricyto-chrome c derivatization of p-type Si with III followed by incorporation of Pt(0) improves photoelectrochemical H2 production efficiency. Strongly interacting reagents can alter semicon-ductor/electrolyte interface energetics and surface state distributions as illustrated by n-type WS2/I-interactions and by differing etch procedures for n-type CdTe. 

Alteration of Interface Energetics and Surface States by Chemical Modification... 

Semiconductor electrodes modified with reagents I-III exhibit properties that are fairly well predicted from the properties associated with the naked semiconductors in contact with ferrocene or Mv2+. Strongly interacting modifiers may alter the interface energetics and surface state distribution in useful ways.(11-14) A classic example of altering surface state distribution comes from electronic devices based on Si.(48) The semiconducting Si has a large density of surface states situated between the valence band and the conduction band. Oxidation of... 

Similarly, if the surface area of a particular interface is altered, the energetics may be handled through a similar idea, namely. 

The chemical and electronic properties of elements at the interfaces between very thin films and bulk substrates are important in several technological areas, particularly microelectronics, sensors, catalysis, metal protection, and solar cells. To study conditions at an interface, depth profiling by ion bombardment is inadvisable, because both composition and chemical state can be altered by interaction with energetic positive ions. The normal procedure is, therefore, to start with a clean or other well-characterized substrate and deposit the thin film on to it slowly at a chosen temperature while XPS is used to monitor the composition and chemical state by recording selected characteristic spectra. The procedure continues until no further spectral changes occur, as a function of film thickness, of time elapsed since deposition, or of changes in substrate temperature. 

The two semiconductor potential distribution conditions most relevant to dye sensitization of planar n-type semiconductors are shown schematically in Figure 2. The flat band-condition applies to the case where the band edges are flat right up to the solution interface (Figure 2a). Under ideal conditions, a positive applied potential does not alter the energetic position of the bands at the semiconductor-... 

Improved understanding of the mechanism, energetics, and structure of the bonding of water to surfaces is needed. Such information is a key to fundamental clarification of the interfacial structure at solid-liquid surfaces. Poor understanding of the thermodynamics of polymer adsorption at interfaces is impeding scientific progress on corrosion inhibition, colloidal stability, alteration of membrane selectivity, and electrocrystallization additives. 

The reason for this state of affairs may be seen in past emphasis on surface phenomenological studies which attempted to model the metal surface as an array of surface atoms with some valences saturated by subsurface metal atoms and other valences saturated by ions or molecules making up the environment. This model led to the description of the interface in terms of the Helmholz and Guy-Chapman double layer theories, and inhibitors were visualized as interfering with the double layer structure through adsorption on the surface atoms of the metal, thereby altering the electrochemical reaction rates which are governed by the energetics of the double layer. While this model has been... 

Some compounds, like short-chain fatty acids, can be soluble in both water and oil because one part of the molecule has an affinity for oil (the nonpolar hydrocarbon chain) and one part has an affinity for water (the polar group). The energetically most favorable orientation for these molecules is at an interface so that each part of the molecnle can reside in the solvent medium for which it has the greatest affinity. These molecules that form oriented monolayers at interfaces show surface activity and are termed surfactants. Some consequences of surfactant adsorption at a surface are that it causes a reduction in surface tension and an alteration in the wettabihty of the surface. Surfactant molar masses range from a few hundreds up to several thousands of grams per mole. 

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